This invention relates to a dispenser having a container vent opening which is positively sealed against leakage therethrough even when slightly nudging the plunger head. More particularly, the pump according to the invention relates to an improvement over my prior U.S. Pat. No. 4,050,613 and is designed to vent accumulated air from the pump chamber directly to the atmosphere for priming or to vent such accumulated air into the container to aid in pump priming. The pump may have a quick opening or a slow opening discharge and make take advantage of compressed air beneath the plunger head for boosting the product in the container to aid in pump priming.
Dispensing pumps are typically provided with a container vent to permit equalization of pressures within and outside the container during pump actuation. However, these container vents are so disposed as to be quite sensitive to opening so that a top load on the plunger will displace the vent seal or other flow passage seal, or both, so as to cause leakage during normal conditions of storage, shipping and handling. Also, a slight nudge of the pump head after the pump is primed is apt to open the vent seal and cause an unwanted leak of the product from the container. An overcap or other means must therefore be provided to hold the plunger in a fully compressed position or in a fully extended position to avoid accidental plunger reciprocation. And, in many of the prior art pumps the container vent opening is located in the wall of the pump chamber and a relief groove or rib is provided in the pump chamber for releasing accumulated air into the atmosphere via the sensitively controlled vent. Little, if any, of this accumulated air is therefore capable of entering the container for boosting the product as an aid in pump priming. And, the opening of the discharge is typically not controlled for quick or slow opening depending on the use intended for the pump or the type of product to be dispensed.